(I) A test of the hypothesis of the primary nature in the colicin transmission mechanism of the colicin El-induced increase in microviscosity of the cell envelope will involve (1) comparison of the rate of the microviscosity increase with those of the ATP and K ion changes. It is proposed to directly measure the rotational rate of the probe through the difference in lifetime of the parallel and perpendicular emission components; and (2) independence of the probe response on ATP and K ion changes, and comparison with colicins K and I. The microviscosity change with known inhibitors of oxidative phosphorylation and electron transport will be determined. (II) The structural basis of the microviscosity increase will be investigated in terms of (1) localization, using envelope fractions, polar and non-polar fluorescence probes, and effects of colicin on the cytochrome b complex; (2) penetration and receptor function, using electron microscopy and probes covalently bound to colicins E1, E2, and E3: and (3) freeze-etch studies of changes in aggregation of intrinsic envelope protein caused by colicin E1. (III) The role of lipid fluidity in the transmission process will be investigated utilizing fatty acid auxotrophs. (IV) Studies on the order-disorder transition in the absence of colicin:. The transition temperature in the order-disorder transition of membrane fractions of wild type cells, fatty acid auxotrophs, col and tol mutants will be determined.